1. Field of the Invention
The invention relates to audio encoding systems (e.g., perceptual encoding systems) and to encoding methods implemented thereby. In a class of embodiments, the invention relates to an audio encoding system configured to generate a single (“unified”) bitstream that is simultaneously compatible with (i.e., decodable by) a first decoder configured to decode audio data encoded in accordance with a first encoding protocol (e.g., multichannel Dolby Digital Plus (E AC-3), or DD+, protocol) and a second decoder configured to decode audio data encoded in accordance with a second encoding protocol (e.g., the AAC, HE AAC v1, or HE AAC v2 protocol).
2. Background of the Invention
Throughout this disclosure including in the claims, the expression performing an operation (e.g., filtering or transforming) “on” signals or data is used in a broad sense to denote performing the operation directly on the signals or data, or on processed versions of the signals or data (e.g., on versions of the signals that have undergone preliminary filtering prior to performance of the operation thereon).
Throughout this disclosure including in the claims, the expression “system” is used in a broad sense to denote a device, system, or subsystem. For example, a subsystem configured to encode data may be referred to as an encoding system (or encoder), and a system including such an encoding subsystem may also be referred to as an encoding system (or encoder).
The expression “encoding protocol” is used herein to denote a set of rules in accordance with which a specific type of encoding is performed. Typically, the rules are set forth in a specification that defines the specific type of encoding.
The expression “decoding protocol” is used herein to denote a set of rules in accordance with which encoded data are decoded, where the encoded data have been encoded in accordance with a specific encoding protocol. Typically, the rules are set forth in a specification that also defines the specific encoding protocol.
Throughout this disclosure including in the claims, the expression “perceptual encoding system” (for encoding audio data determining an audio program that can be rendered by conversion into one or more speaker feeds and conversion of the speaker feed(s) to sound using at least one speaker, said sound having a perceived quality to a human listener) denotes a system configured to compress the audio data in such a manner that, when the inverse of the compression is performed on the compressed data and the resulting decoded data are rendered using the at least one speaker, the resulting sound is perceived by the listener without significant loss in perceived quality. A perceptual encoding system optionally also performs at least one other operation (e.g., upmixing or downmixing) on the audio data in addition to the compression.
Perceptual encoding systems are commonly used to compress (and typically also to downmix or upmix) audio data. Examples of such systems that are in widespread use include the multichannel Dolby Digital Plus (“DD+”) system (compliant with the well-known Enhanced AC-3, or “E AC-3,” digital audio compression protocol adopted by the Advanced Television Systems Committee, Inc.), the MPEG AAC system (compliant with the well-known Advanced Audio Coding or “AAC” audio compression protocol), the HE AAC system (compliant with the well-known MPEG High Efficiency Advanced Audio Coding v1, or “HE AAC v1” audio compression protocol, or the well-known High Efficiency Advanced Audio Coding v2, or “HE AAC v2” audio compression protocol), and the Dolby Pulse system (operable to output a bitstream including DD+(or Dolby Digital) metadata with HE AAC v2 encoded audio, so that an appropriate decoder can extract the metadata from the bitstream and decode the HE AAC v2 audio).
A conventional decoder (known as the Dolby® Multistream Decoder) is capable of decoding either a DD+ encoded bitstream or a Dolby Pulse encoded bitstream. However, this decoder is implemented to be compliant with both the DD+ decoding protocol and the HE AAC v2 decoding protocol, and to extract DD+ (or Dolby Digital) metadata from a Dolby Pulse bitstream. However, a conventional DD+ decoder (compliant with the DD+ decoding protocol but not the HE AAC v2 decoding protocol) could not decode a Dolby Pulse encoded bitstream or a conventional HE AAC v2 encoded bitstream. Nor could a conventional HE AAC v2 decoder (compliant only with the HE AAC v2 decoding protocol but not with the DD+ decoding protocol, and not configured to extract DD+ (or Dolby Digital) metadata from a Dolby Pulse bitstream) decode a DD+ encoded bitstream. Nor could a conventional Dolby Pulse decoder (compliant with the HE AAC v2 decoding protocol and configured to extract DD+ (or Dolby Digital) metadata from a Dolby Pulse bitstream, but not compliant with the DD+ decoding protocol) decode a DD+ bitstream.
It would be desirable to encode audio data in a manner that generates a single bitstream of encoded data that is compatible with (in the sense of being decodable by either) a first conventional decoder configured to decode audio data encoded in accordance with a first conventional encoding protocol (e.g., the DD+ protocol) and a second conventional decoder configured to decode audio data encoded in accordance with a second encoding protocol (e.g., the AAC or HE AAC v2 protocol).
In typical embodiments, the inventive encoder is a key element of a cross-platform audio coding system that efficiently unifies two independent perceptual audio encoding systems into a single encoding system and bitstream format. For example, some embodiments of the inventive encoder combine a DD+ (E AC-3) encoding system and a Dolby Pulse (HE-AAC) encoding system into a single, powerful and efficient perceptual audio encoding system and format, capable of generating a single bitstream that is decodable by either a conventional DD+ decoder or a conventional HE AAC v2 (or HE AAC v1, or AAC) decoder. The bitstream that is output from such embodiments of the inventive encoder is thus compatible with the majority of deployed media playback devices found throughout the world regardless of device type (e.g., AVRs, STBs, Digital Media Adapters, Mobile Phones, Portable Media Players, PCs, etc.).